Indications for Testing

  • Neuromuscular irritability combined with neurologic signs and symptoms
  • Appropriate clinical setting for hypocalcemia (eg, thyroid or previous parathyroid removal)

Laboratory Testing

  • Initial testing – serum calcium and albumin [corrected calcium = measured total calcium +0.8 (4.0-serum albumin)], or use ionized calcium, phosphorus, magnesium, creatinine measurements
  • If calcium low, consider repeat testing with ionized calcium
    • Ionized calcium needs no correction for hypoalbuminemia but should be corrected for pH
  • If hypocalcemia is confirmed, order intact parathyroid hormone (PTH)
    • Elevated PTH, normal or high phosphorus, normal magnesium, high creatinine – consider renal failure/pseudohypoparathyroidism
    • Elevated PTH,  normal or low phosphorus, normal magnesium, normal creatinine – consider vitamin D testing
    • Low PTH, normal or high phosphorus, normal creatinine, low or normal magnesium – consider hypoparathyroidism or hypomagnesemia
    • Normal PTH, normal or low phosphorus, normal creatinine, normal magnesium, low albumin – consider hypoalbuminemia (pseudohypocalcemia)

Differential Diagnosis


  • Serum calcium, phosphorus, and creatinine – measure weekly during initial therapy, then monthly
  • Once stabilized on therapy, measure values 1-2 times/year

Clinical Background

Hypocalcemia may be noted either acutely or chronically in hospitalized patients and outpatients.


  • Prevalence – occurs in 12-80% of critically ill patients



  • Serum calcium concentration kept within a narrow physiologic range
  • Control of calcium by parathyroid hormone, vitamin D (1,25), calcium, and phosphate
  • Calcium is bound to albumin
    • Low levels may reflect hypoalbuminemia, not level of ionized calcium

Clinical Presentation

  • Symptom severity related to rate of change in calcium levels
    • Most patients with mild hypocalcemia are asymptomatic
  • Acute
    • Neuromuscular – tetany, paresthesias, muscle spasms (Chvostek and Trousseau signs), perioral numbness
    • Neuropsychiatric – anxiety, hallucinations, confusion, irritability
    • Cardiovascular – bradycardia, ventricular arrhythmias, congestive heart failure, cardiac collapse
    • Pulmonary – laryngeal stridor, bronchospasm
  • Chronic
    • Neuropsychiatric – cognitive deficits, extrapyramidal symptoms
    • Dermatologic – dermatitis, dry skin, brittle nails
    • Dental – enamel hypoplasia
    • Ophthalmologic – cataracts

Indications for Laboratory Testing

  • Tests generally appear in the order most useful for common clinical situations
  • Click on number for test-specific information in the ARUP Laboratory Test Directory
Test Name and Number Recommended Use Limitations Follow Up
Calcium, Serum or Plasma 0020027
Method: Quantitative Spectrophotometry
Diagnose disorders of calcium metabolism    
Albumin, Serum or Plasma by Spectrophotometry 0020030
Method: Quantitative Spectrophotometry

Order concurrent with calcium to assess for hypoalbuminemia

Calcium, Ionized, Serum 0020135
Method: Ion-Selective Electrode/pH Electrode

Diagnose disorders of calcium metabolism

Abnormal pH will alter results

No correction necessary for hypoalbuminemia

Phosphorus, Inorganic, Plasma or Serum 0020028
Method: Quantitative Spectrophotometry

Evaluate renal function 

Parathyroid Hormone, Intact 0070346
Method: Quantitative Electrochemiluminescent Immunoassay

Diagnose disorders of the parathyroid glands

Magnesium, Plasma or Serum 0020039
Method: Quantitative Spectrophotometry
May help to determine etiology of hypocalcemia    
Vitamin D, 25-Hydroxy 0080379
Method: Quantitative Chemiluminescent Immunoassay

Preferred screening test for vitamin D deficiency

Preferred test to monitor response to supplementation

Additional Tests Available
Click the plus sign to expand the table of additional tests.
Test Name and NumberComments
Creatinine, Serum or Plasma 0020025
Method: Quantitative Enzymatic

Evaluate renal function

Parathyroid Hormone, Intact with Calcium 0070172
Method: Quantitative Electrochemiluminescent Immunoassay

Preferred test to diagnose hypercalcemia, hyperparathyroidism

Calcium, Ionized, Whole Blood 0020140
Method: Ion-Selective Electrode/pH Electrode

Available only to University of Utah patients